1. Field of the Invention
The present invention relates to a recirculating feeder of sheets, in which sheets are supplied from a storing means in which sheets are stacked and stored, and the sheets after being supplied are put back to the storing means again, and more particularly to a recirculating feeder of sheets in a so-called top-pick bottom-return structure in which sheets are supplied from above the stacking direction in the storing means and returned from beneath the stacking direction, which may be favorably applied in a recirculating automatic document feeder (RADF) for conveying the sheet originals sequentially into the exposure region one by one in, for example, an electrostatic copying apparatus.
2. Description of the Prior Art
In an electrostatic copying apparatus, for example, when copying documents in a plurality of sheets, the RADF tends to be installed in order to save the operator's labor of putting the sheets one by one on the original platen. Such RADF conveys the plural sheet originals sequentially to the exposure region having a exposure means in synchronism with the copying action of the electrostatic copying apparatus main body, and realizes the function of, for example, copying duplex originals having images formed on both sides of the sheet on both sides of copying papers, in collaboration with the copying apparatus main body.
Such RADF is provided with a storing means for stacking and storing sheet originals to be copied. Around this storing means there are, among others, a paper feed means for feeding the originals stored in the storing means and starting conveying to the exposure region, and a returning means for returning the originals after exposure in the exposure region back to the storing means. The storing means, and the paper feed means and the returning means around the storing means are collectively called a recirculating original feeding means.
FIG. 1 is a sectional view showing a simplified structure of a typical conventional recirculating original feeding means 1. As stated above, the recirculating original feeding means 1 comprises a storing means 2 for stacking and storing the documents d to be copied, a paper feed means 3 disposed above and at the right side of the storing means 2 in FIG. 1, and a returning means 4 disposed beneath and at the right side of the storing means 2, being composed in a so-called top-pick bottom-return structure.
Hitherto, various structures have been proposed for the paper feed means 3, and the paper feed means 3 in FIG. 3 shows one of these examples. Toward the entire surface of the downstream end in the paper feed direction of the documents d stacked in the storing means 2, air is blown from an exhaust duct 5, and the downstream end in the paper feed direction of the documents d is separated by the air layer. Of the separated documents d, the document d0 at the uppermost position in the stacking direction is sucked and conveyed by a suction conveying means 6 installed above the document d0. The suction conveying means 6 is composed of an endless belt 6c, which possesses innumerable openings and is mounted on two rollers 6a, 6b, and an intake duct 6d disposed at the inner side of the belt 6c. By an intake means which is not shown, when the upper side air of the storing means 2 is sucked in from the openings in the intake duct 6b and the openings of the endless belt 6c, the document d0 at the uppermost position in the stacking direction is attracted to the outer circumference of the endless belt 6c, and is conveyed into a conveying roller 7, and conveyance is started toward the conveying route which is not shown. By the exhaust from the exhaust duct 5, only the separated uppermost document d0 is sucked and conveyed, so that the documents may be supplied into the conveying route securely one by one.
Incidentally, the returning means 4 comprises, for example, rollers 8a, 8b, and an endless belt 9 mounted on the rollers 8a, 8b. This endless belt 9 also serves as the bottom of the storing means 2, and supports the stacked documents d. In the exposure region which is not shown, after the copied document di passes through a conveying route 10, the rollers 8a, 8b are driven to rotate the endless belt 9 in the direction of arrow 13, and the document di is inserted into the lowermost position in the stacking direction of the documents d stacked and stored in the storing means 2. The inserted document di is pressed to the belt 9 by the weight of the documents d being stacked, and is conveyed by the frictional force. The returning means 4 is designed so that the downstream end in the returning direction of the returning document di may be conveyed until reaching a side aligning piece 11 composing the side portion of the storing means 2.
In such construction of the recirculating original feeding means 1, however, the following problems occur. FIG. 2 is a diagram showing the state of the documents d as a problem of the prior art. That is, in the composition of the recirculating original feeding means 1, the documents d are stored in the storing means 2 in such a manner that the vicinity of the upstream side end portion of the returning direction of the documents d may be located in overlap with the returning start point of the returning means 4. In particular, when the exhaust duct 5 is used in the paper feed means 3, air is blown to the lower side by the draft from the exhaust duct 5, in the vicinity of the upstream end in the returning direction of the documents at the lower side of the stacking direction of the stacked documents d. In other words, the vicinity of the upstream end in the returning direction of the documents d stored in the storing means 2 tends to droop into the direction of the conveying route 10 as shown in FIG. 1.
When the document di is returned from the conveying route 10 into the storing means 2 in such state, the vicinity of the upstream end in the returning direction of the documents d in the storing means 2 and the downstream end in the conveying direction of the conveyed document di may collide with each other, and the documents may repel each other, so-called repelling, as shown in FIG. 2 (1), or the returning document may be inserted into an intermediate position, instead of the lowermost position in the stacking direction of the documents d stacked and stored in the storing means 2, so-called mixing, as shown in FIG. 2 (2), thereby causing disorder of documents. When such problems should occur, the conveyed document di is parted from the returning means 4, and is not securely put back into the storing means 2, which may lead to so-called paper jamming.
Besides, when only few documents, for example, two or three are stored in the storing means, as the total weight of the documents to press down the document di conveyed to the belt 9 of the returning means 4 is light, the conveying force (frictional force) of the belt 9 is not transmitted to the document di, so that the document di may not be returned securely until the downstream end in the returning direction of the document di reaches the side end portion 11a of the side aligning piece 11.
Incidentally, in the case of the belt 9 made of rubber or the like, since the frictional force is utilized when returning the document di, static electricity is likely to be generated, and dust particles are likely to stick on the surrounding surfaces. Therefore, such dust deposit may be rubbed against the belt side surface of the document di in the returning step as the belt surface abuts against, so that the document may be stained.
Furthermore, as stated above, when the state of failure of conveyance of the document di up to the side aligning piece continues due to insufficient conveying force, the matching is inferior at the upstream end in the returning direction of the stacked documents d, and the ends are not aligned. In FIG. 1, the upstream end in the returning direction and the downstream end in the paper feed direction are identical, and the air from the exhaust duct 5 is blown against the downstream end in the paper feed direction. Therefore, when the upstream end in the returning direction is misaligned, the air from the exhaust duct 5 is not uniformly blown to the downstream end in the paper feed direction, so that the documents d may not be uniformly separated by the air layer. As a result, as shown in FIG. 2 (3), the document d0 in the uppermost position in the stacking direction is pushed against the documents d side, and the document d0 may not be conveyed by the suction conveying means or supplied obliquely (that is, the paper feed direction and the downstream end in the paper feed direction of documents are not at a right angle).